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intel/compiler: Avoid copy propagating large registers into EOT messages 

EOT messages need to use g112-g127 for their sources.  With the new
opt_split_sends pass, we may be constructing an EOT message from two
different registers, and be able to copy propagate the original values
into those SENDs.

This can cause problems if we copy propagate from a large register
(say an RGBA value which is 4 GRFs in SIMD8 or 8 GRFs in SIMD16), in a
situation where the SEND only read a subset of that (say the alpha value
out of an RGBA texturing result).  g112-127 can only hold 16 registers
worth of data, and sometimes we can only use g112-126.  So, we can't
propagate if the GRFs in question are larger than 15 GRFs.

Fixes a shader validation failure in Alan Wake.  Thanks to Ian Romanick
for catching this!

shader-db on Icelake shows that only SIMD32 programs are affected, and
the results are pretty negligable:

   total instructions in shared programs: 19615228 -> 19615269 (<.01%)
   instructions in affected programs: 10702 -> 10743 (0.38%)
   helped: 1 / HURT: 43 / largest change: +/- 2 instructions

   total cycles in shared programs: 852001706 -> 852001566 (<.01%)
   cycles in affected programs: 767098 -> 766958 (-0.02%)
   helped: 68 / HURT: 64 / largest change: +/- 774 cycles

   GAINED: 2 / LOST: 0

Fixes: 589b03d02f ("intel/fs: Opportunistically split SEND message payloads")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/6803
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17390>
This commit is contained in:
Kenneth Graunke 2022-07-06 20:29:02 -07:00 committed by Marge Bot
parent 983385d319
commit ec2e8bc33f
1 changed files with 23 additions and 4 deletions
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27
src/intel/compiler/brw_fs_copy_propagation.cpp
View File

@ -488,11 +488,30 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
entry->dst, entry->size_written))
return false;
/* Avoid propagating a FIXED_GRF register into an EOT instruction in order
* for any register allocation restrictions to be applied.
/* Send messages with EOT set are restricted to use g112-g127 (and we
* sometimes need g127 for other purposes), so avoid copy propagating
* anything that would make it impossible to satisfy that restriction.
*/
if (entry->src.file == FIXED_GRF && inst->eot)
return false;
if (inst->eot) {
/* Avoid propagating a FIXED_GRF register, as that's already pinned. */
if (entry->src.file == FIXED_GRF)
return false;
/* We might be propagating from a large register, while the SEND only
* is reading a portion of it (say the .A channel in an RGBA value).
* We need to pin both split SEND sources in g112-g126/127, so only
* allow this if the registers aren't too large.
*/
if (inst->opcode == SHADER_OPCODE_SEND && entry->src.file == VGRF) {
int other_src = arg == 2 ? 3 : 2;
unsigned other_size = inst->src[other_src].file == VGRF ?
alloc.sizes[inst->src[other_src].nr] :
inst->size_read(other_src);
unsigned prop_src_size = alloc.sizes[entry->src.nr];
if (other_size + prop_src_size > 15)
return false;
}
}
/* Avoid propagating odd-numbered FIXED_GRF registers into the first source
* of a LINTERP instruction on platforms where the PLN instruction has